The invention is based on a control circuit for an arrangement having at least two direct current motors that can be connected in parallel to a direct voltage system, in particular a circuit for controlling at least two fan motors of a motor vehicle, of the kind used in known circuit arrangements of fan power controllers in motor vehicles. Controlling such motors is done by pulse width modulation of the supply voltage, at a clock frequency typically of approximately 20 kHz; the pulse width ratio determines the motor terminal voltage. The power of the motor, or its torque and rpm, are thus adjusted. The direct current motors here are connected in series with associated power circuit elements between the positive and negative poles of the direct voltage system; one free-wheeling circuit each with a power diode and a common connection back to the positive pole of the direct voltage system via a choke and a further power circuit element is associated with each of the motors. This further power circuit element in the free-wheeling circuit then simultaneously serves to protect against mispolarization for the circuit arrangement and in the event of mispolarization is switched to high impedance.
From German Patent Disclosure DE 103 44 301 A, a control circuit for triggering a single inductive electrical consumer is also known; it has first and second circuit elements, and the first circuit element is connected in series with a resistor element and the consumer between the connection terminals of a direct voltage system. Also here, a second power circuit element is located parallel to the series circuit comprising the resistor element and the first circuit element, and this second power circuit element is controllable by pulse width modulation to adjust the power of the consumer in operation. However, this known control circuit does not disclose any power control for parallel-connected electric motors, nor does it provide any information about possible circuitry for free-wheeling of the motor and for preventing damage from mispolarization upon connection to the direct voltage system. Moreover, the measures taken to detect the motor current are relatively complex and expensive.